1. Field of the Invention
The present invention relates to a brushless DC motor. In particular, the present invention relates to a brushless DC motor with a tray coupling structure.
2. Description of Related Art
FIG. 1 illustrates a conventional brushless DC motor for an optical disc that is disclosed in, e.g., Taiwan Utility Model Publication Nos. 456667 and 590329, and U.S. Pat. No. 6,815,852. Such a brushless DC motor comprises a fixed base 11, a bearing 12, a stator 13, a rotor 14, and a tray 15. The fixed base 11 includes a control circuit and an axial tube 111 in a central portion thereof for receiving the bearing 12 and for supporting the stator 13. The stator 13 is controlled by the control circuit on the fixed base 11 and creates an alternating magnetic field. The rotor 14 includes a shaft 141 rotatably held by the bearing 12 and an annular magnet 142 for induction with the alternating magnetic field to drive the rotor 14 to turn. The tray 15 is coupled to an end of the shaft 141 and driven by the rotor 14. The tray 15 includes a clamping seat 151 for clamping an optical disc.
After mounting the tray 15 onto the shaft 141, the tray 15 is often oblique relative to the shaft 141. To avoid rotational balance of the optical disc and to reduce the disqualified product rate, the bottom face of the tray 15 is grinded to eliminate obliquity of the tray 15. However, the grinding procedure takes a long time, and repetitious tests are required during the grinding procedure. Further, excessive grinding adversely affects the strength and rotational stability of the tray 15.
Taiwan Patent Publication No. 222777 and U.S. Pat. No. 6,700,241 disclose a brushless motor comprising a rotor with a protruded engaging portion in a center of the rotor for engaging with a clamping seat. Thus, an optical disc can be directly loaded on a top face of the rotor. However, adjustment in rotational balance is impossible. In other words, in a case that the rotor is oblique relative to the fixed tube, the axial tube, and the stator, rotational balance could not be obtained. Further, as miniaturization is a trend of spindle motors, it would be impossible for the top face of the rotor having a relatively small area to bear an optical disc.